1. Technical Field
The present invention relates to a light-emitting device, a method for manufacturing the same, and an electronic apparatus.
2. Related Art
There have been light-emitting devices (full-color display devices) for displaying a color image on a screen. Such light-emitting devices include a plurality of pixels that constitute a screen. Each of the pixels includes a plurality of subpixels, and each of the subpixels includes an electroluminescent (EL) element, such as an organic EL element or an inorganic EL element. Examples of such light-emitting devices include RGB light-emitting devices in which each of the pixels includes red, green, and blue subpixels, and RGBW light-emitting devices in which each of the pixels includes red, green, blue, and white subpixels.
Examples of the RGB light-emitting devices include: a first device, in which a light-emitting layer of each of the subpixels is made of an EL material that emit colored light corresponding to the subpixel; a second device, as disclosed in JP-A-2001-57290, in which light-emitting layers of the subpixels are made of an EL material that emits white light, and each of the subpixels includes a color filter with the characteristic corresponding to the color of the subpixel; and a third device, in which light-emitting layers of the subpixels are made of an EL material that emits blue light, and each of the red and green subpixels includes a color-conversion layer with the characteristic corresponding to the color of the subpixel.
An example of the RGBW light-emitting device is a fourth device, in which light-emitting layers of the subpixels are made of an EL material that emits white light, and each of the red, green, and blue subpixels includes a color filter with the characteristic of the corresponding color. The fourth device has a white subpixel in addition to the configuration of the second device. In the fourth device, when a pixel displays white, light emitted from the light-emitting layer of the white subpixel of the pixel is used.
The first device, which requires the use of a polarizing plate for preventing reflection of external light, has low utilization efficiency of emitted light. The second device, which loses a significant portion of the emitted light because of the presence of the color filters, has low utilization efficiency of emitted light. The third device, which requires the use of the color filters to block entrance of unwanted light and loses a portion of the emitted light because of the presence of the color-conversion layers and the color filters, has low utilization efficiency of emitted light. Accordingly the first to third devices have low utilization efficiency of emitted light. In order to realize sufficiently high display quality, the first to third devices have to consume a large amount of power.
The fourth device has a sufficiently high utilization efficiency of emitted light, because, when a pixel displays white, light emitted from the white subpixel of the pixel is output unobstructed. However, when a pixel displays red, green, or blue, the utilization efficiency of emitted light in the fourth device is reduced to 30% or 10%, the same level as the second device, That is, the fourth device has a sufficiently high utilization efficiency of emitted light in the white subpixel but a low utilization efficiency of emitted light in the other subpixels. In order to realize sufficiently high display quality, the fourth device also has to consume a large amount of power.
Now, let us consider a fifth device, which is a modification of the fourth device. In the fifth device as an RGBW light-emitting device, a light-emitting layer of each of the subpixels is made of an EL material that emits colored light corresponding to the subpixel. The fifth device has a sufficiently high utilization efficiency of emitted light in each of the subpixels. However, four types of EL materials need to be used in manufacturing the fifth device. It is clear that the manufacturing process of the fifth device is extremely complex.
Then, let us consider a sixth device, which is an RGB light-emitting device obtained by removing the white subpixel from the fifth device. The sixth device also has a sufficiently high utilization efficiency of emitted light in each of the subpixels. Further, the sixth device only requires three types of EL materials to be used in the manufacturing process. Therefore, the process of manufacturing the sixth device is simplified, compared with the fifth device, but is not sufficiently simple.